Method of manufacturing a transfer mask and method of manufacturing a semiconductor device

ABSTRACT

In a mask blank for manufacturing a transfer mask, the mask blank has a light-shielding film on a transparent substrate. The light-shielding film is made of a material containing tantalum as a main metal component and includes a highly oxidized layer which has an oxygen content of 60 at % or more and which is formed as a surface layer of the light-shielding film. The highly oxidized layer is placed on a side opposite to a transparent substrate side.

CROSS-REFERENCES TO RELATED PATENT APPLICATIONS

This is a Divisional of application Ser. No. 13/076,254 filed Mar. 30,2011, which is a continuation-in-part of U.S. patent application Ser.No. 12/875,783, filed on Sep. 3, 2010, now U.S. Pat. No. 8,435,704,claiming the benefit of priority from Japanese Patent Application No.2010-079327, filed on Mar. 30, 2010, and Japanese Patent Application No.2011-037970, filed on Feb. 24, 2011, the disclosures of which areincorporated herein in their entirety by reference.

TECHNICAL FIELD

This invention relates to a mask blank and a transfer mask improved inchemical resistance and light fastness and further to methods ofmanufacturing them. In particular, this invention relates to a transfermask to be suitably used in an exposure apparatus using exposure lighthaving a short wavelength of 200 nm or less and further to a mask blankfor use in manufacturing such a transfer mask, and further relates tomethods of manufacturing them. This invention also relates to a methodof manufacturing a semiconductor device by the use of theabove-mentioned transfer mask.

BACKGROUND OF THE INVENTION

Generally, fine pattern formation is carried out by photolithography inthe manufacture of a semiconductor device. A number of substrates calledtransfer masks are normally used for such fine pattern formation. Thetransfer mask comprises generally a transparent glass substrate havingthereon a fine pattern made of a metal thin film or the like. Thephotolithography is used also in the manufacture of the transfer mask.

In the manufacture of a transfer mask by photolithography, use is madeof a mask blank having a thin film (e.g. a light-shielding film) forforming a transfer pattern (mask pattern) on a transparent substratesuch as a glass substrate. The manufacture of the transfer mask usingthe mask blank comprises an exposure process of writing a requiredpattern on a resist film formed on the mask blank, a developing processof developing the resist film to form a resist pattern in accordancewith the written pattern, an etching process of etching the thin filmalong the resist pattern, and a process of stripping and removing theremaining resist pattern. In the developing process, a developer issupplied after writing (exposing) the required pattern on the resistfilm formed on the mask blank to dissolve a portion of the resist filmsoluble in the developer, thereby forming the resist pattern. In theetching process, using the resist pattern as a mask, an exposed portionof the thin film, where the resist pattern is not formed, is dissolvedby dry etching or wet etching, thereby forming a required mask patternon the transparent substrate. In this manner, the transfer mask isproduced.

For miniaturization of a pattern of a semiconductor device, it isnecessary to shorten the wavelength of exposure light for use inphotolithography in addition to miniaturization of the mask pattern ofthe transfer mask. In recent years, the wavelength of exposure light foruse in the manufacture of a semiconductor device has been shortened fromKrF excimer laser light (wavelength: 248 nm) to ArF excimer laser light(wavelength: 193 nm).

As the transfer mask, there has conventionally been known a binary maskhaving a light-shielding film pattern made of a chromium-based materialon a transparent substrate.

In recent years, there has also appeared a binary mask for ArF excimerlaser light using a material (MoSi-based material) containing amolybdenum silicide compound as a light-shielding film. This MoSi-basedmaterial may be used as a material of a front-surface antireflectionlayer formed on a light-shielding layer in a light-shielding film(JP-A-2006-78825 (Patent Document 1)). Patent Document 1 proposes, as amaterial of the light-shielding layer of the light-shielding filmcomprising the antireflection layer and the light-shielding layer, amaterial which is composed mainly of tantalum in terms of etchingselectivity to the antireflection layer.

On the other hand, JP-A-S57-161857 (Patent Document 2) discloses a maskblank having a structure in which a tantalum metal layer and a layer ofa mixture of tantalum nitride and tantalum oxide are laminated in thisorder on a transparent substrate.

SUMMARY OF THE INVENTION

In the meantime, since the transfer mask manufacturing cost has beensignificantly increasing following the pattern miniaturization in recentyears, there is an increasing need for a longer lifetime of a transfermask.

As factors that determine the lifetime of a transfer mask, there are aproblem of mask degradation caused by repeated cleaning of the transfermask (problem of chemical resistance) and a problem of mask degradationcaused by cumulative or repetitive irradiation of exposure light on thetransfer mask (problem of light fastness).

A light-shielding film made of a MoSi-based material (particularly, forexample, a light-shielding film having a front-surface antireflectionlayer made of MoSiON containing 10 at % or more Mo) has a problem thatit cannot be said to be good in chemical resistance such as hot waterresistance.

Further, the light-shielding film made of the MoSi-based material has aproblem that it cannot be said to be good in light fastness such as ArFirradiation resistance (ArF irradiation fastness).

Conventionally, for example, when haze (foreign substance composedmainly of ammonium sulfide and generated on a mask) is generated,cleaning is carried out for removing the haze, but a film loss(dissolution of film) due to the cleaning cannot be avoided and thus,roughly, the number of times of cleaning determines the mask lifetime.

As described above, the mask lifetime is shortened if the light fastnessof the light-shielding film is low, but, so far, the light fastness ofthe light-shielding film is obtained within the range of the masklifetime based on the number of times of mask cleaning.

Since the number of times of mask cleaning is reduced due to animprovement to haze in recent years, the period of time of repeated useof a mask is prolonged and thus the exposure time is prolongedcorrespondingly, and therefore, a problem of light fastness particularlyto short-wavelength light such as ArF excimer laser light has been newlyactualized. In the case of a tantalum-based material, the chemicalresistance and the light fastness are high as compared with theMoSi-based material, but the need is high for a further longer lifetimeof a transfer mask and thus higher performance thereof is required. Alsoin the case of a mask for use with KrF excimer laser as an exposurelight, there is a high demand for a further long life and, therefore, ahigher resistance against cleaning is required.

This invention has been made under these circumstances and has an objectto solve the above-mentioned problems that the light-shielding film madeof the MoSi-based material cannot be said to be good in chemicalresistance such as hot water resistance and in light fastness such asArF irradiation resistance, and thus to provide a mask blank and atransfer mask which can ensure excellent chemical resistance and ArFirradiation resistance with a light-shielding film made of atantalum-based material and further to provide methods of manufacturingsuch a mask blank and a transfer mask. Another object of this inventionis to provide a method of manufacturing a semiconductor device by theuse of the above-mentioned transfer mask.

The present inventors have made an intensive study in order to achievethe above-mentioned object.

As a result, the present inventor has found that if a highly oxidizedtantalum layer with an oxygen content of 60 at % or more is formed as asurface layer of a light-shielding film made of a tantalum-basedmaterial, or as a surface layer of a light-shielding film pattern madeof a tantalum-based material and as a surface layer of a sidewall of thepattern, better chemical resistance and ArF irradiation resistance areobtained as compared with a light-shielding film or a light-shieldingfilm pattern made of the tantalum-based material with no such a highlyoxidized tantalum layer.

The present inventors have further found out that a film (highlyoxidized tantalum layer) with more uniform thickness distribution andwith less variation in quality between products can be forcibly formedby applying a later-described predetermined surface treatment (hot watertreatment or the like) to a surface of a light-shielding film made of atantalum-based material, or to a surface of a light-shielding filmpattern made of a tantalum-based material and to a surface of a sidewallof the pattern and, as a result, excellent chemical resistance and ArFirradiation resistance are obtained.

Conventionally, with respect to the light-shielding film made of thetantalum-based material, a study has been made about its composition andits multilayer structure, but has hardly been made about a surface layerof the light-shielding film of the tantalum-based material.

As the light-shielding film made of the tantalum-based material, astructure is known in which, for example, a front-surface antireflectionlayer of TaO is formed on a light-shielding layer of TaN, wherein theoxygen content of the front-surface antireflection layer of TaO is setto 56 to 58 at % for the purpose of enhancing the function of preventingthe front-surface reflection. However, a study has hardly been madeabout a surface layer of the front-surface antireflection layer of TaO.

Under these circumstances, the present inventor has discovered that thelight-shielding film made of the tantalum-based material is oxidized notonly in the case of Ta alone, but also in the case of TaO or TaN.Specifically, as shown in FIG. 10, it has been discovered that, even ina nitrided tantalum film (particularly a highly nitrogenated tantalumfilm), almost all nitrogen is replaced by oxygen in a surface layer ofthe film so that tantalum is oxidized to Ta₂O₅. It has also beendiscovered that oxidation proceeds in a surface layer of a TaO film,resulting in oxidation to Ta₂O₅.

Further, it has been discovered that in the case where a surface layerof a tantalum-based material is naturally oxidized, it takes a long timeof at least more than a year (e.g. 10,000 hours) for a highly oxidizedlayer to grow from the surface layer to the inside so as to bestabilized. It is rare to leave a mask blank formed with alight-shielding film in the atmosphere for more than one year and,particularly, it is even more unthinkable that a transfer mask formedwith a transfer pattern in a light-shielding film is used after beingleft in the atmosphere for more than one year without being used for ArFexposure transfer.

It has been discovered that in the case where a surface layer of atantalum-based material is naturally oxidized, the uniformity inin-plane thickness distribution of a highly oxidized layer and variationin highly oxidized layer thickness between products become large ascompared with the case where the later-described predetermined surfacetreatment according to the present invention is applied.

Particularly, it has been discovered that in the case where a highlyoxidized layer is formed at a sidewall of a light-shielding film patternby natural oxidation in a transfer mask having a light-shielding filmcomprising at least two layers, i.e. a front-surface antireflectionlayer and a light-shielding layer, variation in thickness of the highlyoxidized layer becomes considerably large between the sidewall of thefront-surface antireflection layer made of a material whose oxidationdegree in the formation of the layer is relatively high and the sidewallof the light-shielding layer made of a material whose oxidation degreein the formation of the layer is relatively low, as compared with thecase where a highly oxidized layer is formed by the later-describedpredetermined surface treatment.

Further, it has been discovered that a light-shielding film or alight-shielding film pattern of a tantalum-based material formed with ahighly oxidized layer as its surface layer is excellent in ArFirradiation resistance.

It has further been discovered that in the case where thelater-described predetermined surface treatment is applied, relativelyexcellent chemical resistance and ArF irradiation resistance areobtained as compared with the case where a highly oxidized tantalumlayer with an oxygen content of 60 at % or more (a predetermined highlyoxidized tantalum layer) is not formed as a surface layer of a film. Thereason for this is that when a chemical treatment with acid, alkali orthe like is carried out in the state where the predetermined highlyoxidized tantalum layer is not formed as the surface layer, the film maybe damaged due to dissolution thereof.

The present inventors have found out the above-mentioned facts andcompleted this invention.

In this specification, where appropriate, a highly oxidized tantalumlayer with an oxygen content of 60 at % or more will be referred to as a“predetermined highly oxidized tantalum layer” while an oxidizedtantalum layer with an oxygen content of less than 60 at % will bereferred to as a “tantalum oxide layer”, thereby distinguishing betweenthe two layers.

In this specification, where appropriate, a surface layer of alight-shielding film made of a tantalum-based material, or a surfacelayer of a light-shielding film pattern made of a tantalum-basedmaterial and a surface layer of a sidewall of the pattern will bereferred to as a “predetermined surface layer”.

In this invention, a surface layer represents an outermost surface witha depth of about several nm from the surface plane.

This invention has the following structures.

(Structure 1)

A mask blank for manufacturing a transfer mask, the mask blank having alight-shielding film on a transparent substrate,

wherein the light-shielding film is made of a material containingtantalum as a main metal component, and

a highly oxidized layer with an oxygen content of 60 at % or more isformed as a surface layer of the light-shielding film, that is placed ona side opposite to a transparent substrate side.

(Structure 2)

The mask blank according to the structure 1, wherein the oxygen contentof the highly oxidized layer is 68 at % or more.

(Structure 3)

The mask blank according to the structure 1 or 2, wherein the highlyoxidized layer has a thickness of 1.5 nm or more and 4 nm or less.

(Structure 4)

The mask blank according to any one of the structures 1 to 3, whereinthe highly oxidized layer has Ta₂O₅ bonds at an abundance ratio which ishigher than that of Ta₂O₅ bonds in the light-shielding film except thehighly oxidized layer.

(Structure 5)

The mask blank according to any one of the structures 1 to 4, whereinthe light-shielding film is made of a material further containingnitrogen.

(Structure 6)

The mask blank according to any one of the structures 1 to 3, whereinthe light-shielding film has a structure in which at least alight-shielding layer and a front-surface antireflection layer arelaminated in this order from the transparent substrate side, and

the highly oxidized layer is formed as a surface layer of thefront-surface antireflection layer, that is placed on a side opposite toa light-shielding layer side.

(Structure 7)

The mask blank according to the structure 6, wherein an oxygen contentof the front-surface antireflection layer is lower than the oxygencontent of the highly oxidized layer.

(Structure 8)

The mask blank according to the structure 7, wherein the oxygen contentof the front-surface antireflection layer is 50 at % or more.

(Structure 9)

The mask blank according to any one of the structures 6 to 8, whereinthe highly oxidized layer has Ta₂O₅ bonds at an abundance ratio which ishigher than that of Ta₂O₅ bonds in the front-surface antireflectionlayer.

(Structure 10)

The mask blank according to any one of the structures 6 to 9, whereinthe light-shielding layer is made of a material further containingnitrogen.

(Structure 11)

The mask blank according to any one of the structures 1 to 10, whereinthe light-shielding film has a thickness of less than 60 nm.

(Structure 12)

A transfer mask having a light-shielding film pattern on a transparentsubstrate,

wherein the light-shielding film pattern is made of a materialcontaining tantalum as a main metal component, and

a highly oxidized layer with an oxygen content of 60 at % or more isformed as a surface layer of the light-shielding film pattern, that isplaced on a side opposite to a transparent substrate side and as asurface layer of a sidewall of the light-shielding film pattern.

(Structure 13)

The transfer mask according to the structure 12, wherein the oxygencontent of the highly oxidized layer is 68 at % or more.

(Structure 14)

The transfer mask according to the structure 12 or 13, wherein thehighly oxidized layer has a thickness of 1.5 nm or more and 4 nm orless.

(Structure 15)

The transfer mask according to any one of the structures 12 to 14,wherein the highly oxidized layer has Ta₂O₅ bonds at an abundance ratiowhich is higher than that of Ta₂O₅ bonds in the light-shielding filmpattern except the highly oxidized layer.

(Structure 16)

The transfer mask according to any one of the structures 12 to 15,wherein the light-shielding film pattern is made of a material furthercontaining nitrogen.

(Structure 17)

The transfer mask according to any one of the structures 12 to 14,wherein the light-shielding film pattern has a structure in which atleast a light-shielding layer and a front-surface antireflection layerare laminated in this order from the transparent substrate side.

(Structure 18)

The transfer mask according to the structure 17, wherein an oxygencontent of the front-surface antireflection layer is lower than theoxygen content of the highly oxidized layer.

(Structure 19)

The transfer mask according to the structure 18, wherein the oxygencontent of the front-surface antireflection layer is 50 at % or more.

(Structure 20)

The transfer mask according to any one of the structures 17 to 19,wherein the highly oxidized layer has Ta₂O₅ bonds at an abundance ratiowhich is higher than that of Ta₂O₅ bonds in the front-surfaceantireflection layer.

(Structure 21)

The transfer mask according to any one of the structures 17 to 20,wherein the light-shielding layer is made of a material furthercontaining nitrogen.

(Structure 22)

The transfer mask according to any one of the structures 12 to 21,wherein the light-shielding film pattern has a thickness of less than 60nm.

(Structure 23)

A method of manufacturing a transfer mask having a light-shielding filmpattern on a transparent substrate, the method comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form the light-shielding filmpattern; and

treating the light-shielding film pattern with hot water or ozone waterto form a highly oxidized layer with an oxygen content of 60 at % ormore as a surface layer of the light-shielding film pattern.

(Structure 24)

A method of manufacturing a transfer mask having a light-shielding filmpattern on a transparent substrate, the method comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form the light-shielding filmpattern; and

heat-treating the light-shielding film pattern in a gas containingoxygen to form a highly oxidized layer with an oxygen content of 60 at %or more as a surface layer of the light-shielding film pattern.

(Structure 25)

A method of manufacturing a transfer mask having a light-shielding filmpattern on a transparent substrate, the method comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form the light-shielding filmpattern; and

treating the light-shielding film pattern with ultraviolet lightirradiation in a gas containing oxygen to form a highly oxidized layerwith an oxygen content of 60 at % or more as a surface layer of thelight-shielding film pattern.

(Structure 26)

A method of manufacturing a transfer mask having a light-shielding filmpattern on a transparent substrate, the method comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form the light-shielding filmpattern; and

surface-treating the light-shielding film pattern with oxygen plasma toform a highly oxidized layer with an oxygen content of 60 at % or moreas a surface layer of the light-shielding film pattern.

(Structure 27)

A method of manufacturing a transfer mask having a light-shielding filmpattern on a transparent substrate, the method comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form the light-shielding filmpattern; and

forming a highly oxidized layer with an oxygen content of 60 at % ormore on a surface of the light-shielding film pattern by sputtering.

(Structure 28)

The method of manufacturing a transfer mask according to any one of thestructures 23 to 27, wherein the highly oxidized layer has Ta₂O₅ bondsat an abundance ratio which is higher than that of Ta₂O₅ bonds in thelight-shielding film pattern except the highly oxidized layer.

(Structure 29)

A method of manufacturing a semiconductor device, comprising forming acircuit pattern on a semiconductor wafer by the use of the transfer maskaccording to any one of the structures 12 to 22.

(Structure 30)

A method of manufacturing a semiconductor device, comprising forming acircuit pattern on a semiconductor wafer by the use of the transfer maskprepared by the transfer mask manufacturing method according to any oneof the structures 23 to 28.

(Structure 31)

A mask blank which is used for manufacturing a transfer mask and whichhas a light-shielding film on a transparent substrate,

wherein the light-shielding film is made of a material containingtantalum as a main metal component;

a highly oxidized layer is formed as a surface layer of thelight-shielding film and is placed on a side opposite to a transparentsubstrate side; and

the highly oxidized layer has Ta₂O₅ bonds at an abundance ratio which ishigher than that of Ta₂O₅ bonds in the light-shielding film except thehighly oxidized layer.

(Structure 32)

A transfer mask having a light-shielding film pattern on a transparentsubstrate, wherein:

the light-shielding film pattern is made of a material containingtantalum as a main metal component;

a highly oxidized layer is formed as a surface layer of thelight-shielding film pattern on a side opposite to a transparentsubstrate side and as a surface layer of a side wall of thelight-shielding film pattern; and

the highly oxidized layer has Ta₂O₅ bonds at an abundance ratio which ishigher than that of Ta₂O₅ bonds in the light-shielding film patternexcept the highly oxidized layer.

According to this invention, the following effects are obtained.

(1) Since a highly oxidized tantalum layer with an oxygen content of 60at % or more (a predetermined highly oxidized tantalum layer) is formedas a surface layer of a light-shielding film made of a tantalum-basedmaterial (a predetermined surface layer), or as a surface layer of alight-shielding film pattern made of a tantalum-based material and as asurface layer of a sidewall of the pattern (a predetermined surfacelayer), not only the chemical resistance such as hot water resistance issignificantly improved as compared with a MoSi-based light-shieldingfilm, but also the chemical resistance is improved even as compared witha light-shielding film of the tantalum-based material formed with nosuch a highly oxidized layer.

In the state where a predetermined highly oxidized tantalum layer is notformed as a predetermined surface layer, it may happen that alight-shielding film or a light-shielding film pattern is damaged due toan acid treatment, an alkali treatment, or the like. This damage cannotbe recovered.

(2) In the state where natural oxidation of a surface layer of atantalum-based material has proceeded due to being left in theatmosphere for a long time (more than one year), the chemical resistanceis improved as compared with the case where no such a surface layer isformed. However, the uniformity in thickness distribution of theoxidized layer formed at the surface of a light-shielding film or alight-shielding film pattern decreases as compared with the case where ahighly oxidized tantalum layer is forcibly formed by a surfacetreatment. Further, even when mask blanks manufactured in the same lotare naturally oxidized in the same environment, variation in thicknessof highly oxidized tantalum layers in light-shielding films tends tooccur among the mask blanks. Since detection of the thickness of thehighly oxidized tantalum layer cannot be easily carried out, it isdifficult to perform 100% inspection. That is, it is difficult to stablymanufacture mask blanks having an appropriate highly oxidized tantalumlayer by natural oxidation. On the other hand, in the case where ahighly oxidized tantalum layer is formed by the later-describedpredetermined surface treatment, the uniformity in thicknessdistribution of the highly oxidized tantalum layer is easily obtainedand, further, the uniformity in thickness of highly oxidized tantalumlayers in mask blank products is also high. Accordingly, it is possibleto stably supply mask blanks having a predetermined highly oxidizedtantalum layer.

(3) In a transfer mask, in the state where natural oxidation of asurface layer of a tantalum-based light-shielding film pattern and asurface layer of a sidewall of the pattern has proceeded, the thicknessdistribution of the oxidized layer particularly on the sidewall sidetends to be nonuniform, resulting in the occurrence of portions with lowArF irradiation resistance. On the other hand, in the case where thelater-described predetermined surface treatment is applied after forminga tantalum-based light-shielding film pattern, a predetermined highlyoxidized tantalum layer with highly uniform thickness distribution isformed as a surface layer of the pattern and a surface layer of asidewall of the pattern so that it is possible to provide high ArFirradiation resistance over the entire light-shielding film pattern.

(4) A highly oxidized tantalum layer with an oxygen content of 60 at %or more has higher resistance to Cl-based gas etching as compared with atantalum oxide layer (TaO layer) with an oxygen content of less than 60at % and, therefore, when dry-etching a TaN layer or the like using theTaO layer as a mask, the resistance as the etching mask is improved ascompared with the case where there is no highly oxidized tantalum layerwith an oxygen content of 60 at % or more. Thus, it is possible toreduce rounding of a pattern edge portion of the tantalum oxide layer(front-surface antireflection layer).

(5) In the case where, as in later-described Structure 6, afront-surface antireflection layer is not entirely formed by a highlyoxidized tantalum layer, but only a surface layer thereof is formed by ahighly oxidized tantalum layer, the front-surface antireflection layeris allowed to have a certain optical density for ArF exposure light,thus contributing to a reduction in thickness of a light-shielding film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the structure of a mask blankaccording to an embodiment of this invention;

FIG. 2 is a cross-sectional view showing the structure of a transfermask according to the embodiment of this invention;

FIG. 3 shows cross-sectional views (a) to (g) for describing processesof manufacturing a mask blank and a transfer mask according to theembodiment of this invention;

FIG. 4 is a bright-field (BF) STEM image showing a state, observedbefore ArF irradiation, of a cross-section of a transfer pattern in atransfer mask manufactured in Example 2;

FIG. 5 is a bright-field (BF) STEM image showing a state, observed afterArF irradiation, of a cross-section of a transfer pattern in a transfermask manufactured in Example 2;

FIG. 6 is a dark-field (DF) STEM image showing a state, observed beforeArF irradiation, of a cross-section of a transfer pattern in a transfermask manufactured in Example 2;

FIG. 7 is a dark-field (DF) STEM image showing a state, observed afterArF irradiation, of a cross-section of a transfer pattern in a transfermask manufactured in Example 2;

FIG. 8 is a diagram showing the results of comparing the reflectance(front-surface reflectance) spectra with each other before and after apredetermined surface treatment;

FIG. 9 is a diagram showing the results (depth profile) of analyzing alight-shielding film comprising a TaO antireflection layer and a TaNlight-shielding layer by AES (Auger electron spectroscopy) after apredetermined surface treatment;

FIG. 10 is a diagram showing the results (depth profile) of analyzing ahighly nitrogenated tantalum film by AES;

FIG. 11 is a dark-field (DF) STEM image which shows a cross-section of alight-shielding film in a mask blank according to Example 7;

FIG. 12 shows an electron diffraction image of each area of thelight-shielding film in the mask blank according to Example 7;

FIG. 13 shows Ta4f narrow spectra as a result of XPS analysis of thelight-shielding film in the mask blank according to Example 7;

FIG. 14 shows a result (depth profile) of XPS analysis of alight-shielding film of Example 13 which is formed by a TaBO layer and aTaBN layer;

FIG. 15 shows, as a result of XPS analysis of a light-shielding film ina mask blank according to Example 13, a Ta4f narrow spectrum of a highlyoxidized layer 4;

FIG. 16 shows, as a result of XPS analysis of the light-shielding filmof the mask blank according to Example 13, a Ta4f narrow spectrum of aTaBO layer 3; and

FIG. 17 shows, as a result of XPS analysis of the light-shielding filmof the mask blank according to Example 13, a Ta4f narrow spectrum of aTaBN layer 2.

DESCRIPTION OF THE INVENTION

This invention will be described in detail hereinbelow.

A mask blank according to this invention is for manufacturing a transfermask and is characterized by having a light-shielding film on atransparent substrate,

wherein the light-shielding film is made of a material containingtantalum as a main metal component, and

a highly oxidized layer with an oxygen content of 60 at % or more isformed as a surface layer of the light-shielding film, that is placed ona side opposite to a transparent substrate side (Structure 1).

A transfer mask according to this invention is characterized by having alight-shielding film pattern on a transparent substrate,

wherein the light-shielding film pattern is made of a materialcontaining tantalum as a main metal component, and

a highly oxidized layer with an oxygen content of 60 at % or more isformed as a surface layer of the light-shielding film pattern, that isplaced on a side opposite to a transparent substrate side and as asurface layer of a sidewall of the light-shielding film pattern(Structure 12).

In this invention, the surface layer on the side opposite to thetransparent substrate side represents a layer including a surfacelocated on the side opposite to the transparent substrate side andhaving a certain depth from this surface.

The invention according to the Structure 1 or 12 is an invention basedon the finding that excellent chemical resistance and ArF irradiationresistance are obtained by forming a highly oxidized tantalum layer withan oxygen content of 60 at % or more (a predetermined highly oxidizedtantalum layer) as a surface layer of a light-shielding film made of amaterial containing tantalum as a main metal component (hereinafterreferred to as a “tantalum-based material”) (a predetermined surfacelayer), or as a surface layer of a light-shielding film pattern made ofa tantalum-based material and as a surface layer of a sidewall of thepattern (a predetermined surface layer).

In this invention, it is considered that the bonding state of TaO beinga relatively unstable oxidation state is predominant in a “tantalumoxide layer” formed as a predetermined surface layer when its oxygencontent is less than 60 at %. The oxidation degree of TaO is the lowestamong oxides of tantalum so that a TaO layer is not regarded as a“highly oxidized layer” referred to in this invention.

A tantalum oxide layer with an oxygen content of less than 60 at % isformed as a front-surface antireflection layer. In this event, theoxygen content is, for example, 50 at % or more (e.g. 56 to 58 at %).

It is desirable that the crystal structure of a light-shielding film ofa mask blank or a transfer mask be microcrystalline, preferablyamorphous. This also applies to the light-shielding film of thisinvention. Accordingly, the crystal structure of the light-shieldingfilm hardly becomes a single structure and tends to be in a state wherea plurality of crystal structures are mixed. That is, in the case of ahighly oxidized tantalum layer, it tends to be in a state where TaObonds, Ta₂O₃ bonds, TaO₂ bonds, and Ta₂O₅ bonds are mixed. As the ratioof Ta₂O₅ bonds increases in a predetermined surface layer of thelight-shielding film, the chemical resistance and the ArF irradiationresistance increase while as the ratio of TaO bonds increases, thechemical resistance and the ArF irradiation resistance decrease.

In this invention, it is considered that, in the predetermined highlyoxidized tantalum layer, when its oxygen content is 60 at % or more andless than 66.7 at %, Ta₂O₃ bonds tend to be predominant in the bondingstates of tantalum and oxygen so that the most unstable TaO bondssignificantly decrease as compared with the case where the oxygencontent is less than 60 at %.

In this invention, it is considered that, in the predetermined highlyoxidized tantalum layer, when its oxygen content is 66.7 at % or more,TaO₂ bonds tend to be predominant in the bonding states of tantalum andoxygen so that the most unstable TaO bonds and the next most unstableTa₂O₃ bonds significantly decrease.

In the predetermined highly oxidized tantalum layer, when its oxygencontent is 60 at % or more, not only the most stable state of “Ta₂O₅”,but also the bonding states of “Ta₂O₃” and “TaO₂” are contained.However, it is considered that, at least, the content of the mostunstable TaO bonds reaches a lower limit value, i.e. a value smallenough not to cause a reduction in chemical resistance or ArFirradiation resistance.

In this invention, it is considered that, in the predetermined highlyoxidized tantalum layer, when its oxygen content is 68 at % or more(Structures 2, 13), not only Ta₂O₅ bonds become predominant, but alsothe ratio (namely, presence or abundance ratio) of the bonding state ofTa₂O₅ increases. With such an oxygen content, the bonding states of“Ta₂O₃” and “TaO₂” are rarely present and the bonding state of “TaO”cannot be present. In this invention, it is preferable that the highlyoxidized layer has Ta₂O₅ bonds at an abundance ratio which is higherthan that of Ta₂O₅ bonds in the light-shielding film or thelight-shielding film pattern except the highly oxidized layer(Structures 4, 15). Since Ta₂O₅ bonds form a very stable bonding state,a mask cleaning resistance, such as chemical resistance and hot waterresistance, and ArF irradiation resistance are considerably improved byincreasing the abundance ratio of Ta₂O₅ bonds in the highly oxidizedlayer.

In this invention, it is considered that the predetermined highlyoxidized tantalum layer is formed substantially only by the bondingstate of Ta₂O₅ when its oxygen content is 71.4 at %.

In this invention, the predetermined highly oxidized tantalum layer ismost preferably formed only by the bonding state of Ta₂O₅.

In this invention, when the predetermined highly oxidized tantalum layeris formed only by the bonding state of Ta₂O₅, it is preferable that thepredetermined highly oxidized tantalum layer substantially consists oftantalum and oxygen. This is because the predetermined highly oxidizedtantalum layer is preferably formed substantially only by the bondingstate of Ta₂O₅ and the like.

When the predetermined highly oxidized tantalum layer is substantiallyformed of tantalum and oxygen, it is preferable that nitrogen or anotherelement is contained within a range that does not affect the functionand effect of this invention and is not substantially contained.

In this invention, as a method of forming the highly oxidized tantalumlayer with the oxygen content of 60 at % or more (the predeterminedhighly oxidized tantalum layer), use may be made of a hot watertreatment, an ozone-containing water treatment, a heat treatment in agas containing oxygen, an ultraviolet light irradiation treatment in agas containing oxygen, an O₂ plasma treatment, or the like.

In this invention, the light-shielding film may have a single-layerstructure or a plural-layer structure.

The light-shielding film may comprise an antireflection layer.

The light-shielding film may be a composition gradient film.

The light-shielding film may have a two-layer structure in which alight-shielding layer and a front-surface antireflection layer arelaminated in this order from the transparent substrate side.

The light-shielding film may have a three-layer structure in which aback-surface antireflection layer, a light-shielding layer, and afront-surface antireflection layer are laminated in this order from thetransparent substrate side.

In this invention, the material containing tantalum as the main metalcomponent and forming the light-shielding film may be, for example,tantalum (Ta) alone, tantalum containing nitrogen (TaN), tantalumcontaining oxygen (TaO), tantalum containing nitrogen and oxygen (TaON),tantalum containing boron (TaB), tantalum containing nitrogen and boron(TaBN), tantalum containing oxygen and boron (TaBO), a compositematerial of them, or the like. In addition, carbon (C) may be added to agroup of the above-mentioned materials.

In this invention, the highly oxidized tantalum layer with the oxygencontent of 60 at % or more (the predetermined highly oxidized tantalumlayer) preferably has a thickness of 1.5 nm or more and 4 nm or less(Structure 3, 14).

If the thickness is less than 1.5 nm, it is too thin to expect theeffect while if the thickness exceeds 4 nm, it largely affects thefront-surface reflectance, thus making it difficult to perform controlfor obtaining a predetermined front-surface reflectance (reflectance forArF exposure light or reflectance spectrum for lights with respectivewavelengths). Further, since the highly oxidized tantalum layer is verylow in optical density for ArF exposure light, the optical density thatcan be obtained by the front-surface antireflection layer is reduced,thus adversely affecting in terms of reducing the thickness of thelight-shielding film.

In the case where the highly oxidized tantalum layer is formed byapplying a later-described predetermined surface treatment immediatelyafter forming the light-shielding film or in a state of no naturaloxidation after forming the light-shielding film, the thickness of thehighly oxidized tantalum layer tends to be in the range of 1.5 nm to 4nm. If the thickness is in this range, sufficient chemical resistanceand ArF irradiation resistance are obtained. Taking into account thebalance between the viewpoint of ensuring the optical density of theentire light-shielding film and the viewpoint of improving the chemicalresistance and the ArF irradiation resistance, the thickness of thehighly oxidized tantalum layer is more preferably set to 1.5 nm or moreand 3 nm or less.

According to an aspect of this invention, the light-shielding film orthe light-shielding film pattern is made of a material furthercontaining nitrogen (Structure 5 or 16).

This structure is advantageous in terms of preventing the back-surfacereflection and, since a back-surface antireflection layer for preventingthe back-surface reflection does not need to be formed between thetransparent substrate and the light-shielding layer, it is advantageousalso in terms of ensuring the light-shielding performance with arelatively small thickness.

In another aspect of this invention, the light-shielding film has astructure in which at least a light-shielding layer and a front-surfaceantireflection layer are laminated in this order from the transparentsubstrate side, and

the highly oxidized layer is formed as a surface layer of thefront-surface antireflection layer, that is placed on a side opposite toa light-shielding layer side (Structure 6).

In another aspect of this invention, the light-shielding film patternmay have a structure in which at least a light-shielding layer and afront-surface antireflection layer are laminated in this order from thetransparent substrate side (Structure 17).

This structure is advantageous in terms of preventing the front-surfacereflection and, by forming the light-shielding layer of a material withhigh light-shielding performance, it is advantageous also in terms ofensuring the light-shielding performance with a relatively smallthickness.

In this invention, it is preferable that an oxygen content of thefront-surface antireflection layer is lower than the oxygen content ofthe highly oxidized layer (Structure 7, 18).

This structure is advantageous in terms of obtaining a predeterminedfront-surface reflectance with a smaller thickness.

In this invention, the oxygen content of the front-surfaceantireflection layer is preferably less than 60 at %.

In this invention, it is preferable that the oxygen content of thefront-surface antireflection layer is 50 at % or more (Structure 8, 19).

This structure is advantageous in terms of enhancing (maximizing) theeffect of preventing the front-surface reflection. Further, when thefront-surface antireflection layer is used as an etching mask (hardmask) in dry etching of the light-shielding layer using a chlorine-basedgas, the etching resistance to the chlorine-based gas increases so thathigher etching selectivity can be ensured. In the case where thefront-surface antireflection layer further contains nitrogen, the totalcontent of nitrogen and oxygen is preferably 50 at % or more and, evenif the oxygen content falls below 50 at %, the effect of preventing thefront-surface reflection can still be enhanced.

In terms of enhancing (maximizing) the effect of preventing thefront-surface reflection, it is preferable that, for example, the oxygencontent of the front-surface antireflection layer be set to 56 to 58 at% and the highly oxidized tantalum layer with the oxygen content of 60at % or more be formed as a surface layer of the front-surfaceantireflection layer.

In Structures 6 to 8 and 17 to 19, It is preferable that the highlyoxidized layer has Ta₂O₅ bonds at an abundance ratio which is higherthan that of Ta₂O₅ bonds in the front-surface antireflection layer(Structures 9, 20).

Since the Ta₂O₅ bonds are an extremely stable bonding state, the maskcleaning resistance, such as the chemical resistance and the hot waterresistance, and the ArF irradiation resistance are remarkably improvedby increasing the abundance ratio of Ta₂O₅ bonds in the highly oxidizedlayer.

In the above-mentioned Structures 6 to 9, Structures 17 to 20, it ispreferable that the light-shielding layer is made of a material furthercontaining nitrogen (Structure 10, 21).

This structure is advantageous in terms of preventing the back-surfacereflection and also in terms of ensuring the light-shielding performanceof the light-shielding film with a relatively small thickness.

It is preferable that the light-shielding film or the light-shieldingfilm pattern has a thickness of less than 60 nm (Structure 11, 22).

These structures are advantageous in terms of transferring a finerpattern.

Particularly for a transfer mask for use in the hyper-NA exposure(immersion exposure) generation, it is necessary to perform mask patterncorrection such as OPC (optical proximity correction) or SRAF(sub-resolution assist feature). In order to reduce calculation load ofa simulation necessary for such correction, it is effective to reducethe thickness of a mask pattern and this can be satisfied by theabove-mentioned structure.

The present inventor has elucidated that a first treatment after forminga light-shielding film or after forming a light-shielding film patternby etching the light-shielding film largely affects the chemicalresistance and the ArF irradiation resistance and thus is important(Structures 23 to 26).

The present inventor has discovered that if the first treatment is notappropriate, the light-shielding film or the light-shielding filmpattern may be damaged. For example, it has been discovered that if thefirst treatment is a treatment using an alkaline solution such as anaqueous solution containing ammonia and hydrogen peroxide, thelight-shielding film or the light-shielding film pattern may be damaged(particularly, if a TaN layer is included, the TaN layer is damaged).Further, it has been discovered that, for example, in the case where thelight-shielding film contains boron, if the first treatment is an acidtreatment using a sulfuric acid hydrogen peroxide mixture, hotconcentrated sulfuric acid, or the like, the light-shielding film or thelight-shielding film pattern may be damaged.

The present inventor has discovered that one or more of a hot watertreatment, an ozone-containing water treatment, a heat treatment in agas containing oxygen, an ultraviolet light irradiation treatment in agas containing oxygen, and a surface treatment with oxygen plasma aresuitable as the first treatment.

A uniform and strong film (highly oxidized tantalum layer) can beforcibly formed by applying the above-mentioned predetermined surfacetreatment and, as a result, excellent chemical resistance and ArFirradiation resistance are obtained.

The above-mentioned predetermined surface treatment can also serve as acleaning treatment.

Since it has been elucidated that a highly oxidized tantalum layer of apredetermined thickness can be formed as a surface layer of thelight-shielding film pattern by applying the above-mentionedpredetermined surface treatment, confirmation by analysis is notrequired in the case where the above-mentioned predetermined surfacetreatment is applied. On the other hand, in the case of naturaloxidation, the progress of the oxidation is largely affected by anenvironment in which a substrate formed with a light-shielding filmpattern is left, and thus it is difficult to control the thickness of asurface layer of the light-shielding film pattern. Currently, there isno particular method for detecting the thickness of a highly oxidizedtantalum layer in a short time and with no destruction and thus it isdifficult to perform 100% inspection. Further, in the case of naturaloxidation, more than one year (e.g. 10,000 hours) is required so thatdifficulty arises also in terms of the production management.

A method of manufacturing a transfer mask according to this invention isfor manufacturing a transfer mask having a light-shielding film patternon a transparent substrate, and is characterized by comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form a light-shielding film pattern;and

treating the light-shielding film pattern with hot water or ozone waterto form a highly oxidized layer with an oxygen content of 60 at % ormore as a surface layer of the light-shielding film pattern (Structure23).

The treatment with the hot water preferably uses pure water or ultrapurewater such as deionized water (DI water).

The temperature of the hot water is preferably about 70 to 90° C.

The treatment time with the hot water is preferably about 10 to 120minutes.

The treatment with the ozone water preferably uses 40 to 60 ppmozone-containing water.

The temperature of the ozone-containing water is preferably about 15 to30° C.

The treatment time with the ozone-containing water is preferably about10 to 20 minutes.

A method of manufacturing a transfer mask according to this invention isfor manufacturing a transfer mask having a light-shielding film patternon a transparent substrate, and is characterized by comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form a light-shielding film pattern;and

heat-treating the light-shielding film pattern in a gas containingoxygen to form a highly oxidized layer with an oxygen content of 60 at %or more as a surface layer of the light-shielding film pattern(Structure 24).

The temperature of the heat treatment is preferably about 120 to 280° C.

The treatment time of the heat treatment is preferably about 5 to 30minutes.

As the gas containing oxygen, use may be made of the atmosphere, anatmosphere with an oxygen concentration higher than that of theatmosphere, or the like.

A method of manufacturing a transfer mask according to this invention isfor manufacturing a transfer mask having a light-shielding film patternon a transparent substrate, and is characterized by comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form a light-shielding film pattern;and

treating the light-shielding film pattern with ultraviolet lightirradiation in a gas containing oxygen to form a highly oxidized layerwith an oxygen content of 60 at % or more as a surface layer of thelight-shielding film pattern (Structure 25).

Ultraviolet light for use in the ultraviolet light irradiation treatmentmay have any wavelength as long as it can produce ozone from oxygencontained in the gas (the atmosphere) around a surface of thelight-shielding film pattern. Monochromatic short-wavelength ultravioletlight such as KrF excimer laser light, ArF excimer laser light, Xe₂excimer laser light or Xe₂ excimer light is preferable because it canefficiently produce ozone from ambient oxygen and minimize the heatgeneration of the light-shielding film irradiated with the ultravioletlight.

In the case of the excimer laser light, the irradiation range is narrowdue to the properties thereof so that it is necessary to scan thesurface of the light-shielding film pattern. Therefore, the irradiationtime of the ultraviolet light irradiation treatment cannot beunconditionally specified, but is, for example, preferably about 15 to30 minutes. On the other hand, in the case of ultraviolet lightirradiation using an ultrahigh pressure mercury lamp, the irradiationtime is preferably about 1 to 10 minutes.

The gas containing oxygen may be an atmospheric state or an atmospherewith an oxygen concentration higher than that of the atmospheric state,or the like.

A method of manufacturing a transfer mask according to this invention isfor manufacturing a transfer mask having a light-shielding film patternon a transparent substrate, and is characterized by method comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form a light-shielding film pattern;and

surface-treating the light-shielding film pattern with oxygen plasma toform a highly oxidized layer with an oxygen content of 60 at % or moreas a surface layer of the light-shielding film pattern (Structure 26).

The treatment time with the oxygen plasma is preferably about 1 to 10minutes.

A method of manufacturing a transfer mask according to this invention isfor manufacturing a transfer mask having a light-shielding film patternon a transparent substrate, and is characterized by comprising:

forming, on the transparent substrate, a light-shielding film made of amaterial containing tantalum as a main metal component;

etching the light-shielding film to form a light-shielding film pattern;and

forming a highly oxidized layer with an oxygen content of 60 at % ormore on a surface of the light-shielding film pattern by sputtering(Structure 27).

In this invention, when Ta is used as a target, a tantalum film with anoxygen content of 60 at % or more is difficult to form by a low defectby DC magnetron sputtering, and it is preferable to use RF magnetronsputtering or ion beam sputtering.

Particularly, in the case of forming a predetermined surface layer usinga Ta₂O₅ target, the film formation is difficult by DC magnetronsputtering because Ta₂O₅ has no conductivity, and it is necessary to useRF magnetron sputtering or ion beam sputtering.

Even in the case of forming a predetermined surface layer by RFmagnetron sputtering or ion beam sputtering using a Ta₂O₅ target, thesurface layer may be subjected to oxygen deficiency (bonding state otherthan Ta₂O₅ bonding state is present) in an atmosphere of only a noblegas as a film forming gas introduced into a sputtering chamber. In orderto avoid this, it is preferable that the surface layer be formed byintroducing, as a film forming gas, a mixed gas of a noble gas andoxygen into the sputtering chamber.

In Structures 23 to 27, it is preferable that the highly oxidized layerhas Ta₂O₅ bonds at an abundance ratio which is higher than that of Ta₂O₅bonds in the front-surface antireflection layer (Structure 28).

This is because, since the Ta₂O₅ bonds are an extremely stable bondingstate, the mask cleaning resistance, such as the chemical resistance andthe hot water resistance, and the ArF irradiation resistance areconsiderably improved by increasing the abundance ratio of Ta₂O₅ bondsin the highly oxidized layer.

According to Structures 1 to 32, mask cleaning resistance, such aschemical resistance and hot water resistance, and ArF irradiationfastness are considerably improved. Therefore, the invention describedin Structures 1 to 32 is particularly suitable to a transfer mask and amask blank adapted to exposure light having a wavelength of 200 nm orless.

According to Structures 1 to 32, mask cleaning resistance, such aschemical resistance and hot water resistance, is considerably improved.Therefore, the invention described in Structures 1 to 32 is particularlysuitable to a transfer mask and a mask blank adapted to KrF excimerlaser exposure light (having a wavelength of 248 nm).

In this invention, sputtering is preferably used as a method of formingthe light-shielding film, but this invention is not limited thereto.

A DC magnetron sputtering apparatus is preferably used as a sputteringapparatus, but this invention is not limited to this film formingapparatus. Another type of sputtering apparatus such as a RF magnetronsputtering apparatus may alternatively be used.

In this invention, dry etching effective for forming a fine pattern ispreferably used as the above-mentioned etching.

In this invention, use can be made of, for example, a fluorine-based gassuch as SF₆, CF₄, C₂F₆, or CHF₃ in dry etching of a tantalum-basedmaterial containing oxygen (tantalum oxide layer, highly oxidizedtantalum layer, or the like).

In this invention, use can be made of, for example, a fluorine-based gassuch as SF₆, CF₄, C₂F₆, or CHF₃, a mixed gas of such a fluorine-basedgas and He, H₂, N₂, Ar, C₂H₄, O₂, or the like, a chlorine-based gas suchas Cl₂ or CH₂Cl₂, or a mixed gas of such a chlorine-based gas and He,H₂, N₂, Ar, C₂H₄, or the like.

In this invention, the transparent substrate is not particularly limitedas long as it has transparency with respect to an exposure wavelength tobe used. In this invention, a synthetic quartz substrate, a quartzsubstrate, and various other glass substrates (e.g. CaF₂ substrate,soda-lime glass substrate, aluminosilicate glass substrate, alkali-freeglass substrate, low thermal expansion glass substrate, etc.) can beused and, among them, the synthetic quartz substrate is particularlysuitable for this invention because it has high transparency in therange of ArF excimer laser light or shorter-wavelength light.

A method of manufacturing a semiconductor device according to thisinvention is featured by forming a circuit pattern on a semiconductorwafer by using the transfer mask mentioned in any one of the structuresor the transfer mask manufactured by the method mentioned in any one ofthe structures (Structures 29, 30).

The light-shield film pattern of the transfer mask according to thisinvention is excellent in the hot water resistance, the chemicalresistance, and so on and also in the ArF irradiation resistance.Therefore, decrease of a line width during mask cleaning is small and anincrease of the line width due to irradiation of the ArF excimer laseris small. Accordingly, it is possible to transfer a fine pattern (forexample, a circuit pattern of DRAM hp 45 nm) onto a resist film on asemiconductor wafer with high accuracy. Consequently, the fine patterncan be formed on the semiconductor wafer with high accuracy by using aresist pattern which is formed by exposure transfer using the transfermask according to this invention.

A mask blank according to this invention is used for manufacturing thetransfer mask and comprises a light-shielding film on a transparentsubstrate, wherein:

the light-shielding film is made of a material containing tantalum as amain metal component;

a highly oxidized layer is formed as a surface layer of thelight-shielding film and is placed on a side opposite to a transparentsubstate side; and

the highly oxidized layer has Ta₂O₅ bonds at an abundance ratio which ishigher than that of Ta₂O₅ bonds in the light-shielding film except thehighly oxidized layer (Structure 31).

A transfer mask according to this invention has a light-shielding filmpattern on a transparent substrate and is featured in that:

the light-shielding film pattern is made of a material containingtantalum as a main metal component;

a highly oxidized layer is formed as a surface layer of thelight-shielding film pattern on a side opposite to a transparentsubstrate side and as a surface layer of a side wall of thelight-shielding film pattern; and

the highly oxidized layer has Ta₂O₅ bonds at an abundance ratio which ishigher than that of Ta₂O₅ bonds in the light-shielding film patternexcept the hightly oxidized layer (Structure 32).

The light-shielding film and the light-shielding film pattern of themask blank and the transfer mask mentioned above are excellent in thechemical resistance, the hot water resistance, and the ArF irradiationresistance because the highly oxidized layer which has a high abundanceratio of Ta₂O₅ bonds is formed as the surface layer.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 is a cross-sectional view showing the structure of a mask blankaccording to an embodiment of this invention, FIG. 2 is across-sectional view showing the structure of a transfer mask accordingto the embodiment of this invention, and FIG. 3 is a cross-sectionalview showing processes of manufacturing a mask blank and a transfer maskaccording to the embodiment of this invention. Hereinbelow, referring tothese figures, the mask blank and the transfer mask according to theembodiment of this invention will be described.

As shown in FIG. 1, the mask blank according to this embodiment isconfigured such that a Ta nitride layer (light-shielding layer) 2composed mainly of Ta nitride and having a thickness of 42 nm is formedon a glass substrate 1 made of synthetic quartz, a Ta oxide layer(front-surface antireflection layer) 3 composed mainly of Ta oxide andhaving a thickness of 9 nm is formed on the Ta nitride layer 2, and ahighly oxidized tantalum layer 4 is formed as a surface layer of the Taoxide layer 3. The Ta nitride layer 2, the Ta oxide layer 3, and thehighly oxidized tantalum layer 4 form a light-shielding film 30. Thenitrogen (N) content of the Ta nitride layer 2 is 16 at %, the oxygen(O) content of the Ta oxide layer 3 is 58 at %, and the oxygen (O)content of the highly oxidized tantalum layer 4 is 71.4 at %.

As shown in FIG. 2, the transfer mask according to this embodiment isconfigured such that, by patterning the light-shielding film 30 of themask blank shown in FIG. 1, a fine pattern comprising a portion 30 awhere the light-shielding film 30 is left remaining and a portion 30 bwhere the light-shielding film 30 is removed is formed on the glasssubstrate 1.

A highly oxidized tantalum layer 4 a is formed as a surface layer of thelight-shielding film pattern 30 a. Further, at a sidewall of thelight-shielding film pattern 30 a, a highly oxidized tantalum layer 4 bis formed as a surface layer of a sidewall of a pattern 3 a of the Taoxide layer 3 and a highly oxidized tantalum layer 4 c is formed as asurface layer of a sidewall of a pattern 2 a of the Ta nitride layer 2.

Referring now to FIG. 3, a description will be given of Examples ofmanufacturing the mask blank and the transfer mask according to thisembodiment.

EXAMPLE 1 Manufacture of Mask Blank: Hot Water Treatment

A substrate 1 made of synthetic quartz and having a size of about 152mm×152 mm square and a thickness of 6.35 mm was introduced into a DCmagnetron sputtering apparatus. After the inside of the sputteringapparatus was evacuated to 2×10⁻⁵ (Pa) or less, a mixed gas of Ar and N₂was introduced into the sputtering apparatus. In this event, the flowrate of Ar and the flow rate of N₂ were adjusted to 38.5 sccm and 9sccm, respectively. Ta was used as a sputtering target. After the gasflow rates were stabilized, the power of a DC power supply was set to1.5 kW, thereby forming a Ta nitride layer 2 having a thickness of 42 nmon the substrate 1 (see FIG. 3, (a)).

Then, while the substrate 1 formed with the Ta nitride layer 2 wasmaintained in the sputtering apparatus, a mixed gas containing an Ar gasat a flow rate of 58 sccm and an O₂ gas at a flow rate of 32.5 sccm wasintroduced into the sputtering apparatus and then the power of the DCpower supply was set to 0.7 kW, thereby stacking a Ta oxide layer 3having a thickness of 9 nm on the Ta nitride layer 2 (see FIG. 3, (b)).When forming the Ta oxide layer 3 by DC magnetron sputtering, it mayhappen that an oxide film is deposited on the sputtering target toreduce the film forming rate. For suppressing the reduction in filmforming rate, a DC pulse unit is effective. In this Example, use wasmade of Sparc-LE V (trade name) manufactured by Advanced EnergyIndustries, Inc.

The reflectance (front-surface reflectance) of a surface, remote fromthe substrate 1, of a light-shielding film 30 thus formed was 25.2% forArF exposure light (wavelength: 193 nm). The reflectance (back-surfacereflectance) of a surface, where the light-shielding film 30 was notformed, of the substrate 1 was 38.2% for ArF exposure light. Further,the transmittance for ArF exposure light was 0.1%.

Values of refractive index n and extinction coefficient k werecalculated using n&k 1280 (trade name), an optical thin-film propertymeasuring apparatus, manufactured by n&k Technology, Inc. As a result,the refractive index n and the extinction coefficient k of the Tanitride layer 2 were 2.00 and 2.22, respectively, and the refractiveindex n and the extinction coefficient k of the Ta oxide layer 3 were2.23 and 1.09, respectively.

Further, analysis by AES (Auger electron spectroscopy) was performed fora light-shielding film 30 formed in the same manner. As a result, thenitrogen (N) content of the Ta nitride layer 2 was 16 at % and theoxygen (O) content of the Ta oxide layer 3 was 58 at %. At this point oftime, the formation of a highly oxidized tantalum layer 4 was notconfirmed.

Further, the surface roughness in a 1 μm square area of thelight-shielding film 30 was measured using AFM (atomic force microscope)and, as a result, the surface roughness Rms was 0.29 nm.

Further, defect inspection was conducted using M1350 (trade name), adefect inspection apparatus, manufactured by Lasertec Corporation and itwas confirmed that it was possible to identify defects normally.

Before natural oxidation proceeded (e.g. within one hour after the filmformation) or after being kept in an environment where natural oxidationdid not proceed, a mask blank thus manufactured was immersed indeionized water (DI water) at 90° C. for 120 minutes, thereby carryingout a hot water treatment (surface treatment).

In this manner, a mask blank of Example 1 was obtained.

In the mask blank of Example 1, the formation of a highly oxidizedtantalum layer 4 was confirmed at a surface layer of the light-shieldingfilm 30. Specifically, the highly oxidized tantalum layer (Ta₂O₅ layer)4 having a thickness of 2 nm was confirmed by a depth profile of thelight-shielding film in AES analysis results as shown in FIG. 9. Theoxygen (O) content of this layer 4 was 71.4 to 67 at %.

In the mask blank of Example 1, the reflectance (front-surfacereflectance) of a surface, remote from the substrate 1, of thelight-shielding film 30 was 25.1% for ArF exposure light (wavelength:193 nm) and thus a change was small with respect to the front-surfacereflectance before the surface treatment. The reflectance (back-surfacereflectance) of a surface, where the light-shielding film 30 was notformed, of the substrate 1 was 38.2% for ArF exposure light and thus wasthe same as that before the surface treatment. Further, thetransmittance for ArF exposure light was 0.1% and thus was the same asthat before the surface treatment.

Further, the surface roughness in a 1 μm square area of thelight-shielding film 30 was measured using AFM. As a result, the surfaceroughness Rms was 0.29 nm and thus was the same as that before thesurface treatment.

Further, defect inspection was conducted using M1350 (trade name)manufactured by Lasertec Corporation and it was confirmed that it waspossible to identify defects normally.

As shown in FIG. 8, the reflectance (front-surface reflectance) spectrabefore and after the hot water treatment were compared with each other.As a result, the reflectance was slightly lowered (about 0.5% to 1%)around 250 nm. It is thus conjectured that it is possible to change theproperties (e.g. improve the stoichiometry) of the highly oxidizedtantalum layer 4 by the hot water treatment.

REFERENCE EXAMPLE 1 Mask Blank is Left in the Atmosphere

A light-shielding film 30 was formed in the same manner as in Example 1.Then, before natural oxidation proceeded (e.g. within one hour after thefilm formation) or after being kept in an environment where naturaloxidation did not proceed, a mask blank was left in an environment at25° C. and 40% RH for 1,000 hours (about 42 days), thereby causingnatural oxidation to proceed.

In this manner, a mask blank of Reference Example 1 was obtained.

In the mask blank of Reference Example 1, the formation of a highlyoxidized tantalum layer 4 was confirmed at a surface layer of thelight-shielding film 30. Specifically, the highly oxidized tantalumlayer 4 having a thickness of 1 nm was confirmed by a depth profile ofthe light-shielding film in AES analysis results. This layer 4 wasanalyzed by AES and, as a result, the oxygen (O) content changed from71.4 at % to 59 at % from the side opposite to the transparent substrateside toward the light-shielding layer side, thus forming a compositiongradient structure.

(Evaluation of Mask Blank)

There were prepared a plurality of mask blanks of Example 1, a pluralityof mask blanks of Reference Example 1, and a plurality of mask blanks(Comparative Example 1) immediately after the film formation of alight-shielding film 30 in the same manner as in Example 1, i.e. nothaving been subjected to a forcible oxidation treatment such as a hotwater treatment or natural oxidation. Then, the chemical resistance ofthese mask blanks was verified. The verification was performed by anacid treatment and an alkali treatment which were widely used in maskcleaning or the like. In the acid treatment, a solution of [sulfuricacid (H₂SO₄, concentration 98 wt %):hydrogen peroxide (H₂O₂,concentration 30 wt %)=4:1 (volume ratio)] was heated to 90° C. andused. The treatment time was set to 30 minutes. In the alkali treatment,a solution of [ammonium hydroxide (NH₄OH, concentration 25 wt%):hydrogen peroxide (H₂O₂, concentration 30 wt %):water (H₂O)=2:1:4(volume ratio)] was used at room temperature (23° C.). The treatmenttime was set to 30 minutes.

As a result, with respect to the light-shielding film 30 of the maskblank of Comparative Example 1, a film loss of a little less than 0.2 nmwas confirmed as a result of the acid treatment while a film loss ofabout 0.3 nm was confirmed as a result of the alkali treatment. Withrespect to the light-shielding film 30 of the mask blank of ReferenceExample 1, a film loss of a little less than 0.2 nm was confirmed as aresult of the acid treatment while a film loss of a little less than 0.3nm was confirmed as a result of the alkali treatment. Thus, there wasalmost no effect with the highly oxidized tantalum layer 4 having acomposition gradient structure with insufficient oxidation and having athickness of as small as about 1 nm. On the other hand, with respect tothe light-shielding film 30 of the mask blank of Example 1, no film losswas confirmed (below the lower detection limit) as a result of either ofthe chemical treatments, i.e. the acid treatment and the alkalitreatment. Thus, it was seen that the highly oxidized tantalum layer 4largely contributed to the improvement in chemical resistance.

EXAMPLE 2 Manufacture of Transfer Mask: Hot Water Treatment

A light-shielding film 30 was formed in the same manner as in Example 1.Then, a transfer mask of Example 2 was manufactured using a mask blankbefore natural oxidation proceeded (e.g. within one hour after the filmformation) or after being kept in an environment where natural oxidationdid not proceed.

First, an electron beam resist 5 was coated to a thickness of 150 nm(see FIG. 3, (c)) and then electron beam writing and development werecarried out, thereby forming a resist pattern 5 a (see FIG. 3, (d)).

Then, dry etching using a fluorine-based (CHF₃) gas was carried out,thereby forming a pattern 3 a of a Ta oxide layer 3 (see FIG. 3, (e)).Then, dry etching using a chlorine-based (Cl₂) gas was carried out,thereby forming a pattern 2 a of a Ta nitride layer 2. Further, 30%additional etching was carried out, thereby forming a light-shieldingfilm pattern 30 a on a substrate 1 (see FIG. 3, (f)).

SEM cross-section observation was carried out for the light-shieldingfilm pattern 30 a thus formed. As a result, the electron beam resistremained with a thickness of about 80 nm.

Then, the resist on the light-shielding film pattern 30 a was removed,thereby obtaining the light-shielding film pattern 30 a as a transferpattern (see FIG. 3, (g)).

In this manner, a transfer mask (binary mask) was obtained.

Before natural oxidation proceeded (e.g. within one hour after thetransfer pattern formation) or after being kept in an environment wherenatural oxidation did not proceed, the transfer mask thus manufacturedwas immersed in deionized water (DI water) at 90° C. for 120 minutes,thereby carrying out a hot water treatment (surface treatment).

In this manner, a transfer mask of Example 2 was obtained.

In the transfer mask of Example 2, the formation of highly oxidizedtantalum layers 4 a, 4 b, and 4 c was confirmed at a surface layer ofthe light-shielding film pattern 30 a. Specifically, the highly oxidizedtantalum layers 4 a, 4 b, and 4 c each having a thickness of 3 nm wereconfirmed by cross-section observation using STEM (scanning transmissionelectron microscope). AES analysis was also performed at a portion,where the light-shielding film was present, of the light-shielding filmpattern 30 a. Based on a depth profile of the light-shielding film inAES analysis results, it was confirmed that the oxygen (O) content ofthe highly oxidized tantalum layer 4 a as a surface layer of the Taoxide layer 3 was 71.4 to 67 at %. On the other hand, it is difficult toconfirm the oxygen content at a pattern sidewall portion by AESanalysis. Therefore, EDX (energy dispersive X-ray spectroscopy) analysiswas used at the time of the observation by STEM to make comparison withthe results of the preceding AES analysis on the highly oxidizedtantalum layer 4 a as the surface layer of the light-shielding filmpattern 30 a. As a result, it was confirmed that the oxygen contents ofthe highly oxidized tantalum layers 4 b and 4 c were each equal to thatof the highly oxidized tantalum layer 4 a.

EXAMPLE 3 Manufacture of Transfer Mask: Ozone Treatment

A transfer mask was obtained by forming a light-shielding film pattern30 a in a light-shielding film 30 of a mask blank of Example 1 in thesame manner as in Example 2. Then, before natural oxidation proceeded(e.g. within one hour after the transfer pattern formation) or afterbeing kept in an environment where natural oxidation did not proceed,the transfer mask not having been subjected to a hot water treatment wassubjected to an ozone treatment, thereby manufacturing a transfer maskof Example 3.

The ozone treatment (surface treatment) was carried out usingozone-containing water with an ozone concentration of 50 ppm and at atemperature of 25° C. The treatment time was set to 15 minutes.

In this manner, the transfer mask of Example 3 was obtained.

In the transfer mask of Example 3, the formation of highly oxidizedtantalum layers 4 a, 4 b, and 4 c was confirmed at a surface layer ofthe light-shielding film pattern 30 a. Specifically, the highly oxidizedtantalum layers 4 a, 4 b, and 4 c each having a thickness of 3 nm wereconfirmed by cross-section observation using STEM. AES analysis was alsoperformed at a portion, where the light-shielding film was present, ofthe light-shielding film pattern 30 a. Based on a depth profile of thelight-shielding film in AES analysis results, it was confirmed that theoxygen (O) content of the highly oxidized tantalum layer 4 a as asurface layer of a Ta oxide layer 3 was 71.4 to 67 at %. On the otherhand, it is difficult to confirm the oxygen content at a patternsidewall portion by AES analysis. Therefore, EDX analysis was used atthe time of the observation by STEM to make comparison with the resultsof the preceding AES analysis on the highly oxidized tantalum layer 4 aas the surface layer of the light-shielding film pattern 30 a. As aresult, it was confirmed that the oxygen contents of the highly oxidizedtantalum layers 4 b and 4 c were each equal to that of the highlyoxidized tantalum layer 4 a.

EXAMPLE 4 Manufacture of Transfer Mask: Heat Treatment

A transfer mask was obtained by forming a light-shielding film pattern30 a in a light-shielding film 30 of a mask blank of Example 1 in thesame manner as in Example 2. Then, before natural oxidation proceeded(e.g. within one hour after the transfer pattern formation) or afterbeing kept in an environment where natural oxidation did not proceed,the transfer mask not having been subjected to a hot water treatment wassubjected to a heat treatment, thereby manufacturing a transfer mask ofExample 4.

The heat treatment (surface treatment) was carried out at a heatingtemperature of 140° C. in the atmosphere for a treatment time of 30minutes.

In this manner, the transfer mask of Example 4 was obtained.

In the transfer mask of Example 4, the formation of highly oxidizedtantalum layers 4 a, 4 b, and 4 c was confirmed at a surface layer ofthe light-shielding film pattern 30 a. Specifically, the highly oxidizedtantalum layers 4 a, 4 b, and 4 c each having a thickness of 3 nm wereconfirmed by cross-section observation using STEM. AES analysis was alsoperformed at a portion, where the light-shielding film was present, ofthe light-shielding film pattern 30 a. Based on a depth profile of thelight-shielding film in AES analysis results, it was confirmed that theoxygen (O) content of the highly oxidized tantalum layer 4 a as asurface layer of a Ta oxide layer 3 was 71.4 to 67 at %. On the otherhand, it is difficult to confirm the oxygen content at a patternsidewall portion by AES analysis. Therefore, EDX analysis was used atthe time of the observation by STEM to make comparison with the resultsof the preceding AES analysis on the highly oxidized tantalum layer 4 aas the surface layer of the light-shielding film pattern 30 a. As aresult, it was confirmed that the oxygen contents of the highly oxidizedtantalum layers 4 b and 4 c were each equal to that of the highlyoxidized tantalum layer 4 a.

EXAMPLE 5 Manufacture of Transfer Mask: UV Light Irradiation Treatment

A transfer mask was obtained by forming a light-shielding film pattern30 a in a light-shielding film 30 of a mask blank of Example 1 in thesame manner as in Example 2. Then, before natural oxidation proceeded(e.g. within one hour after the transfer pattern formation) or afterbeing kept in an environment where natural oxidation did not proceed,the transfer mask not having been subjected to a hot water treatment wassubjected to an ultraviolet light irradiation treatment, therebymanufacturing a transfer mask of Example 5.

The ultraviolet light irradiation treatment (surface treatment) wascarried out by scanning 50 mJ/cm² ArF excimer laser light at a scanningspeed of 1 cm/sec over the entire surface of the light-shielding filmpattern 30 a.

In this manner, the transfer mask of Example 5 was obtained.

In the transfer mask of Example 5, the formation of highly oxidizedtantalum layers 4 a, 4 b, and 4 c was confirmed at a surface layer ofthe light-shielding film pattern 30 a. Specifically, the highly oxidizedtantalum layers 4 a, 4 b, and 4 c each having a thickness of 3 nm wereconfirmed by cross-section observation using STEM. AES analysis was alsoperformed at a portion, where the light-shielding film was present, ofthe light-shielding film pattern 30 a. Based on a depth profile of thelight-shielding film in AES analysis results, it was confirmed that theoxygen (O) content of the highly oxidized tantalum layer 4 a as asurface layer of a Ta oxide layer 3 was 71.4 to 67 at %. On the otherhand, it is difficult to confirm the oxygen content at a patternsidewall portion by AES analysis. Therefore, EDX analysis was used atthe time of the observation by STEM to make comparison with the resultsof the preceding AES analysis on the highly oxidized tantalum layer 4 aas the surface layer of the light-shielding film pattern 30 a. As aresult, it was confirmed that the oxygen contents of the highly oxidizedtantalum layers 4 b and 4 c were each equal to that of the highlyoxidized tantalum layer 4 a.

EXAMPLE 6 Manufacture of Transfer Mask: Oxygen Plasma Treatment

A transfer mask was obtained by forming a light-shielding film pattern30 a in a light-shielding film 30 of a mask blank of Example 1 in thesame manner as in Example 2. Then, before natural oxidation proceeded(e.g. within one hour after the transfer pattern formation) or afterbeing kept in an environment where natural oxidation did not proceed,the transfer mask not having been subjected to a hot water treatment wassubjected to an oxygen plasma treatment, thereby manufacturing atransfer mask of Example 6.

The oxygen plasma treatment (surface treatment) was carried out byintroducing the transfer mask into a resist stripping apparatus adaptedto perform oxygen plasma ashing. The treatment time was set to 5minutes.

In this manner, the transfer mask of Example 6 was obtained.

In the transfer mask of Example 6, the formation of highly oxidizedtantalum layers 4 a, 4 b, and 4 c was confirmed at a surface layer ofthe light-shielding film pattern 30 a. Specifically, the highly oxidizedtantalum layers 4 a, 4 b, and 4 c each having a thickness of 3 nm wereconfirmed by cross-section observation using STEM. AES analysis was alsoperformed at a portion, where the light-shielding film was present, ofthe light-shielding film pattern 30 a. Based on a depth profile of thelight-shielding film in AES analysis results, it was confirmed that theoxygen (O) content of the highly oxidized tantalum layer 4 a as asurface layer of a Ta oxide layer 3 was 71.4 to 67 at %. On the otherhand, it is difficult to confirm the oxygen content at a patternsidewall portion by AES analysis. Therefore, EDX analysis was used atthe time of the observation by STEM to make comparison with the resultsof the preceding AES analysis on the highly oxidized tantalum layer 4 aas the surface layer of the light-shielding film pattern 30 a. As aresult, it was confirmed that the oxygen contents of the highly oxidizedtantalum layers 4 b and 4 c were each equal to that of the highlyoxidized tantalum layer 4 a.

REFERENCE EXAMPLE 2 Transfer Mask is Left in the Atmosphere

A transfer mask was obtained by forming a light-shielding film pattern30 a in a light-shielding film 30 of a mask blank of Example 1 in thesame manner as in Example 2. Then, before natural oxidation proceeded(e.g. within one hour after the transfer pattern formation) or afterbeing kept in an environment where natural oxidation did not proceed,the transfer mask not having been subjected to a hot water treatment wassubjected to natural oxidation, thereby manufacturing a transfer mask ofReference Example 2.

Specifically, the transfer mask was left in an environment at 25° C. and40% RH for 1,000 hours (about 42 days), thereby causing naturaloxidation to proceed.

In this manner, the transfer mask of Reference Example 2 was obtained.

In the transfer mask of Reference Example 2, the formation of highlyoxidized tantalum layers 4 a, 4 b, and 4 c was confirmed at a surfacelayer of the light-shielding film pattern 30 a. Specifically, the highlyoxidized tantalum layers 4 a, 4 b, and 4 c each having a thickness ofabout 1 nm were confirmed by cross-section observation using STEM. AESanalysis was also performed at a portion, where the light-shielding filmwas present, of the light-shielding film pattern 30 a. Based on a depthprofile of the light-shielding film in AES analysis results, it wasconfirmed that the oxygen (O) content of the highly oxidized tantalumlayer 4 a as a surface layer of a Ta oxide layer 3 changed from 71.4 at% to 59 at % from the side opposite to the transparent substrate sidetoward the light-shielding layer side, thus forming a compositiongradient structure.

(Evaluation of Transfer Mask)

There were prepared a plurality of transfer masks of each of Examples 2to 6 and Reference Example 2 and a plurality of transfer masks(Comparative Example 2) each of which was obtained by forming alight-shielding film pattern 30 a in a light-shielding film 30 of a maskblank of Example 1 in the same manner as in Example 2, each of which wasin a state before natural oxidation proceeded (e.g. within one hourafter the transfer pattern formation) or after being kept in anenvironment where natural oxidation did not proceed, and each of whichwas not subjected to a hot water treatment. Then, the chemicalresistance of these transfer masks was verified. The verification wasperformed by an acid treatment and an alkali treatment which were widelyused in mask cleaning or the like. In the acid treatment, a solution of[sulfuric acid (H₂SO₄, concentration 98 wt %):hydrogen peroxide (H₂O₂,concentration 30 wt %)=4:1 (volume ratio)] was heated to 90° C. andused. The treatment time was set to 30 minutes. In the alkali treatment,a solution of [ammonium hydroxide (NH₄OH, concentration 25 wt%):hydrogen peroxide (H₂O₂, concentration 30 wt %):water (H₂O)=2:1:4(volume ratio)] was used at room temperature (23° C.). The treatmenttime was set to 30 minutes.

As a result, with respect to the light-shielding film pattern 30 a ofthe transfer mask of Comparative Example 2, a film loss of a little lessthan 0.2 nm was confirmed as a result of the acid treatment while a filmloss of about 0.3 nm was confirmed as a result of the alkali treatment.With respect to the light-shielding film pattern 30 a of the transfermask of Reference Example 2, a film loss of a little less than 0.2 nmwas confirmed as a result of the acid treatment while a film loss of alittle less than 0.3 nm was confirmed as a result of the alkalitreatment. Thus, there was almost no effect with the highly oxidizedtantalum layers 4 a, 4 b, and 4 c having a composition gradientstructure with insufficient oxidation and having a thickness of as smallas about 1 nm. On the other hand, with respect to the light-shieldingfilm patterns 30 a of the transfer masks of Examples 2 to 6, no filmloss was confirmed (below the lower detection limit) as a result ofeither of the chemical treatments, i.e. the acid treatment and thealkali treatment. Thus, it was seen that the highly oxidized tantalumlayers 4 a, 4 b, and 4 c largely contributed to the improvement inchemical resistance.

Then, likewise, there were prepared transfer masks of Examples 2 to 6,Reference Example 2, and Comparative Example 2. Then, ArF excimer laserlight (wavelength: 193 nm) with a pulse frequency of 300 Hz and a pulseenergy of 16 mJ/cm²/pulse was continuously irradiated so that thecumulative dose became 30 kJ/cm². Herein, the dose of 30 kJ/cm²corresponds to a dose which is received by a transfer mask whenexposing/transferring a transfer pattern to resist films of 112,500wafers.

In the case of the transfer masks manufactured in Examples 2 to 6, i.e.in the case where the hot water treatment, the ozone treatment, the heattreatment in a gas containing oxygen, the ultraviolet light irradiationtreatment in a gas containing oxygen, and the surface treatment withoxygen plasma were applied to the transfer patterns, respectively,before natural oxidation of the transfer patterns proceeded (e.g. withinone hour after the transfer pattern formation) or after being kept in anenvironment where natural oxidation of the transfer patterns did notproceed, ArF irradiation resistance, which will be described withreference to FIGS. 4 and 5 and FIGS. 6 and 7, was obtained.

FIGS. 4 and 5 and FIGS. 6 and 7 are STEM photographs showing states,observed before and after ArF irradiation, of cross-sections of thetransfer patterns in the transfer masks manufactured in Example 2. FIGS.4 and 5 are each a bright-field (BF) STEM image (magnification:×500,000) which is formed using electron beams transmitted through thesample, wherein FIG. 4 shows a cross-section of the transfer maskirradiated with no ArF excimer laser light while FIG. 5 shows across-section of the transfer mask irradiated with 30 kJ/cm² of ArFexcimer laser light in a 50% RH environment. FIGS. 6 and 7 are each adark-field (DF) STEM image (magnification: ×500,000) which is formedusing electron beams scattered from the sample and which enablesobservation of a composition image in which the contrast reflecting thecomposition of the sample is obtained. FIG. 6 shows a cross-section ofthe transfer mask irradiated with no ArF excimer laser light and is thedark-field STEM image of the same transfer mask as FIG. 4. FIG. 7 showsa cross-section of the transfer mask irradiated with 30 kJ/cm² of ArFexcimer laser light in a 50% RH environment and is the dark-field STEMimage of the same transfer mask as FIG. 5.

In the bright-field STEM images of FIGS. 4 and 5, a portion close toblack is the light-shielding film pattern 30 a and an underlying patternof a lighter color than the light-shielding film pattern 30 a is thetransparent substrate 1. In order to better observe the shape of thesidewall of the light-shielding film pattern 30 a, the transparentsubstrate 1 is intentionally dug down by etching. In the dark-fieldimages of FIGS. 6 and 7, the pattern 3 a of the Ta oxide layer 3 and thepattern 2 a of the Ta nitride layer 2 of the light-shielding filmpattern 30 a can be better observed visually. As shown in FIGS. 4 and 5and FIGS. 6 and 7, in comparison with the ArF non-irradiation state(reference) of FIGS. 4 and 6, no difference (degradation such asincrease in line width, change in surface layer of the antireflectionlayer, or change in optical density) was observed after the irradiationwith 30 kJ/cm² of ArF excimer laser light in FIGS. 5 and 7. The sameverification was performed for the transfer masks of Examples 3 to 6 andthe results were as good as Example 2. The same verification wasperformed also for the transfer masks of Comparative Example 2 andReference Example 2 and the results were not so good as Examples 2 to 6.

As described above, it is seen that the transfer masks (binary masks)and the mask blanks (binary mask blanks) of the Examples have extremelyhigh light fastness to cumulative irradiation of exposure light having ashort wavelength of 200 nm or less.

COMPARATIVE EXAMPLE 3 <MoSi-Based Light-Shielding Film>

On a substrate 1 made of synthetic quartz and having a size of about 152mm×152 mm square and a thickness of 6.35 mm, a MoSiN film(light-shielding layer) 2 and a MoSiON film (front-surfaceantireflection layer) 3 were formed in this order as a light-shieldingfilm 30 using a DC magnetron sputtering apparatus (see FIG. 3, (a) and(b) which are used for the sake of description).

Specifically, using a mixed target of Mo and Si (Mo:Si=21 at %:79 at %),a film comprising molybdenum, silicon, and nitrogen (Mo:9 at %, Si:72.8at %, N:18.2 at %) was formed to a thickness of 52 nm in an Ar gasatmosphere, thereby forming the MoSiN film (light-shielding layer) 2.

Then, using a mixed target of Mo:Si=12 mol %:88 mol %, a film comprisingmolybdenum, silicon, oxygen, and nitrogen (Mo:7.4 at %, Si:52.3 at %,O:16.1 at %, N:24.2 at %) was formed to a thickness of 8 nm in a mixedgas atmosphere of Ar, O₂, and N₂, thereby forming the MoSiON film(front-surface antireflection layer) 3.

The total thickness of the light-shielding film 30 was 60 nm. Theoptical density (OD) of the light-shielding film 30 was 3.0 at thewavelength 193 nm of ArF excimer laser exposure light.

In this manner, a binary mask blank of Comparative Example 3 wasmanufactured.

Then, a binary mask was manufactured using this binary mask blank.

First, a chemically amplified positive resist film 5 for electron beamwriting (PRL009 manufactured by FUJIFILM Electronic Materials Co., Ltd.)was formed on the mask blank (see FIG. 3, (c)).

Then, using an electron beam writing apparatus, a required pattern waswritten on the resist film 5 formed on the mask blank and, thereafter,the resist film 5 was developed with a predetermined developer, therebyforming a resist pattern 5 a (see FIG. 3, (d)).

Then, using the resist pattern 5 a as a mask, the two-layer structurelight-shielding film 30 comprising the MoSiN film (light-shieldinglayer) 2 and the MoSiON film (front-surface antireflection layer) 3 wasdry-etched, thereby forming a light-shielding film pattern 30 a (seeFIG. 3, (e) and (f)). A mixed gas of SF₆ and He was used as a dryetching gas.

Then, the remaining resist pattern was stripped, thereby obtaining abinary mask of Comparative Example 3 (see FIG. 3, (g)).

There was almost no change in optical density (OD) of thelight-shielding film at the wavelength 193 nm of ArF excimer laserexposure light as compared with that at the time of the manufacture ofthe mask blank.

Then, ArF excimer laser light with a pulse frequency of 300 Hz and apulse energy of 16 mJ/cm²/pulse was continuously irradiated onto theobtained binary mask so that the cumulative dose became 30 kJ/cm².Herein, the dose of 30 kJ/cm² corresponds to a dose which is received bya transfer mask when exposing/transferring a transfer pattern to resistfilms of 112,500 wafers.

The optical density (OD) of the light-shielding film after theirradiation was measured. As a result, it was less than 3.0 at thewavelength 193 nm of ArF excimer laser exposure light and thus areduction in optical density was observed. Further, as a result ofobserving in detail a cross-section of the light-shielding film patternusing STEM, a modified layer was confirmed and an increase in line width(CD change) due to the modified layer was also confirmed to be 15 nm.

Further, like in Example 1, the obtained masks were immersed in anammonia hydrogen peroxide mixture and hot water, respectively, therebyexamining the chemical resistance (ammonia hydrogen peroxide mixtureresistance and hot water resistance) thereof, particularly the chemicalresistance of a pattern sidewall. As a result, corrosion of the patternsidewall was confirmed in both cases.

Further, as a result of observing in detail a mask surface after theirradiation, deposits were confirmed on the glass substrate or the filmdue to precipitation of Mo.

EXAMPLE 7 Manufacture of Mask Blank: Heat Treatment

On a substrate 1 made of synthetic quartz and having a size of about 152mm×152 mm square and a thickness of 6.35 mm, a Ta nitride layer 2 wasdeposited to a thickness of 42 nm by the use of a DC magnetronsputtering apparatus. Deposition of the Ta nitride layer 2 was carriedout by reactive sputtering by using Ta as a sputter target in a mixedgas atmosphere of Xe and N₂ (see FIG. 3( a)). Next, a Ta oxide layer 3was deposited to a thickness of 9 nm onto the Ta nitride layer 2 whilethe substrate 1 with the Ta nitride layer 2 deposited thereon was heldin the sputtering apparatus. Deposition of the Ta oxide layer 3 wasperformed by reactive sputtering by using Ta as a sputter target in amixed gas atmosphere of Ar and O₂ (see FIG. 3( b)).

Thus, a light-shielding film 30 comprising the Ta nitride layer 2 andthe Ta oxide layer 3 was formed on the substrate 1. At a surface of thelight-shielding film 30, the reflectance (front-surface reflectance) forArF exposure light (wavelength: 193 nm) was 24.8%. At a back surface ofthe substrate 1 without the light-shielding film 30, the reflectance(back-surface reflectance) for ArF exposure light was 37.8%. Thetransmittance for ArF exposure light was 0.1%. The light-shielding film30 was subjected to AES (Auger Electron Spectroscopy) analysis. As aresult, the content of nitrogen (N) in the Ta nitride layer 2 was 16 at% and the content of oxygen (O) in the Ta oxide layer 3 was 58 at %.Subsequently, before progress of natural oxidation (for example, withinone hour after the film deposition) or after the mask blank afterdeposition of the light-shielding film 30 was held in an environmentwithout causing natural oxidization to progress, the mask blank thusmanufactured was subjected to a heat treatment (surface treatment) inthe ambient atmosphere at a heating temperature of 200° C. for atreating time of 5 minutes.

The mask blank thus manufactured was subjected to cross-sectionalobservation by the use of a STEM (Scanning Transmission ElectronMicroscope). FIG. 11 shows a dark-field (DF) image of thelight-shielding film 30, taken by the STEM. From the dark-field (DF)image, it has been confirmed that the light-shielding film 30 had ahighly oxidized layer 4 of 3 nm thick as a surface layer. By using thespecimen inspected by the STEM, an electron beam (a focused beam havinga beam diameter of about 1 nm) was irradiated onto a surface of asectional plane of the light-shielding film 30 from a directionperpendicular to the sectional plane to obtain electron diffractionimages. FIG. 12 shows the electron diffraction images of an analysispoint 1 (shown by “□1” in FIG. 11), an analysis point 2 (shown by “□2”in FIG. 11), and an anlysis point 3 (shown by “□3” in FIG. 11). It hasbeen confirmed from the electron diffraction images that the analysispoint 1 in a region of the highly oxidized layer 4 had an amorphousstructure while the analysis point 2 in a region of the Ta oxide layer 3had a mixed state of an amorphous structure and a microcrystallinestructure. It has been also confirmed from the electron diffractionimage that the analysis point 3 in a region of the Ta nitride layer 2had a microcrystalline structure.

Subsequently, the light-shielding film 30 was subjected to an XPS (X-rayPhotoelectron Spectroscopy) analysis. FIG. 13 shows, as a result of theXPS analysis, Ta4f narrow spectra of the light-shielding film 30. Fromthe result shown in FIG. 13, it is seen that the narrow spectrum of anuppermost surface layer of the light-shielding film 30 has a high peakat a position of the binding energy (25.4 eV) of T₂O₅. Therefore, it isunderstood that the abundance ratio of T₂O₅ bonds is high in theuppermost layer. In the narrow spectrum of a layer (the region of thehighly oxidized layer 4) placed at the depth of 1 nm from the surface ofthe light-shielding film 30, a single peak is observed at a glance.However, this spectrum was obtained as a result of superposition of apeak at a position of the binding energy (25.4 eV) of Ta₂O₅ and anotherpeak at a position of the binding energy (21.0 eV) of Ta. The peak ofthe spectrum is considerably close to the position of the binding energyof Ta₂O₅. This shows that the abundance ratio of Ta₂O₅ bonds in thislayer is high, although it is lower than that of Ta₂O₅ bonds in theuppermost surface layer.

On the other hand, in the narrow spectrum of a layer (the region of theTa oxide layer 3) placed at the depth of 5 nm from the surface of thelight-shielding film 30, a single peak is observed at a glance. Again,this spectrum was obtained as a result of superposition of a peak at aposition of the bining energy (25.4 eV) of Ta₂O₅ and a peak at aposition of the binding energy (21.0 eV) of Ta. However, the peak of thespectrum is slightly closer to the position of the binding energy of Taand the abundance ratio of Ta₂O₅ bonds is not high in this layer. Inaddition, in the narrow spectrum of a layer (the region of the Tanitride layer 2) placed at the depth of 15 nm from the surface of thelight-shielding film 30, a peak is present near the position of thebinding energy (21.0 eV) of Ta. This suggests that the Ta nitride layerhas a nitrogen content of 16 at % and is relatively low in nitridationdegree and the binding energy of the Ta nitride is close to the bindingenergy of Ta. This is obvious also from the fact that the binding energyof TaN(N:50 at %) is 23.0 eV and the binding energy of Ta₂N(N:about 33at %) is 22.6 eV and thus the binding energy becomes closer to thebinding energy of Ta as the nitrogen content decreases.

As described above, it is understood from the result of the AESananlysis for the light-shielding film 30 of Example 1 and the result ofthe XPS analysis for the light-shielding film 30 of Example 7 that, inthe light-shielding film 30, each of the Ta oxide layer 3, the inside ofthe highly oxidized layer 4, and the uppermost layer of the highlyoxidized layer 4 has the oxygen content of 60 at % or more and that theoxygen content in the light-shielding film 30 increases towards thesurface. Furthermore, it is obvious that, towards the surface, the peakof the Ta4f narrow spectrum is shifted to a higher energy side and theabundance ratio of the Ta₂O₅ bonds in the film becomes higher.

EXAMPLES 8 TO 12 Manufacture of a Transfer Mask, Manufacture of aSemiconductor Device

Transfer masks according to Examples 8 to 12 were manufactured by theuse of mask blanks obtained by depositing a light-shielding film 30 in amanner similar to that of Example 7 and carrying out a heat treatment(surface treatment) within the ambient atmosphere at a heatingtemperature of 200° C. for a processing time of 5 minutes.

At first, an electron beam resist 5 was applied to each mask blank to athickness of 100 nm (see FIG. 3( c)) and electron beam lithography anddevelopment were carried out to form a resist pattern 5 a having acircuit pattern of DRAM hp45 nm (see FIG. 3( d)).

Next, dry etching was carried out by the use of a fluorine-based gas(CF₄ gas) to form a pattern 3 a of a Ta oxide layer 3 (see FIG. 3( e)).Thereafter, dry etching was performed by the use of chlorine-based gas(Cl₂) to form a pattern 2 a of the Ta nitride layer 2. Further,additional etching of 40% was conducted to form a light-shielding filmpattern 30 a on a substrate 1 (FIG. 3( f)).

Subsequently, the resist pattern 5 a on the light-shielding film pattern30 a was removed. Thus, the light-shielding film pattern 30 a having afunction as a transfer mask was obtained (FIG. 3( g)).

As described above, the plural transfer masks (binary masks) weremanufactured.

Then, the transfer mask manufactured as mentioned above was subjected toa hot water treatment (surface treatment) like in Example 2 to obtain atransfer mask according to Example 8. Another transfer mask manufacturedas mentioned above was subjected to an ozone treatment like in Example 3to obtain a transfer mask according to Example 9. Still another transfermask manufactured as mentioned above was subjected to a heat treatmentlike in Example 4 to obtain a transfer mask according to Example 10. Yetanother transfer mask manufactured as mentioned above was subjected toan ultraviolet irradiation treatment like in Example 5 to obtain atransfer mask according to Example 11. Yet still another transfer maskmanufactured as mentioned above was subjected an oxygen plasma treatmentlike in Example 6 to obtain a transfer mask according to Example 12.

For each of the transfer masks thus manufactured according to Examples 8to 12, it has been confirmed that highly oxidized layers 4 a, 4 b, and 4c of tantalum (Ta) were formed as a surface layer of the light-shieldingfilm pattern 30 a. Specifically, the highly oxidized layers 4 a, 4 b,and 4 c of 3 nm thick were confirmed by cross-sectional observationconducted by a STEM (Scanning Transmission Electron Microscope). Thelight-shielding film pattern 30 a was subjected to AES (Auger ElectronSpectroscopy) analysis at a portion where the light-shielding film wasleft. As a result of the analysis, a profile of the light-shielding filmin a depth direction was obtained. From the profile, it has beenconfirmed that the highly oxidized layer 4 a of tantalum as a surfacelayer of the Ta oxide layer 3 had the oxygen content of 71.4 to 67 at %Furthermore, a side wall portion of the light-shielding film pattern 30a was subjected to EDX (Energy Dispersive X-ray spectroscopy) analysisduring observation by the STEM. The result of the EDX analysis wascompared with the result of the previously-conducted AES analysis forthe highly oxidized layer 4 a as the surface layer of thelight-shielding film pattern 30 a. As a consequence, it has beenconfirmed that the oxygen content of the highly oxidized layer 4 a wasequal to those of the highly oxidized layers 4 b and 4 c.

Furthermore, the light-shielding film pattern 30 a of each of thetransfer masks according to Examples 8 to 12 was subjected to XPS (X-rayPhotoelectron Spectroscopy) analysis in a manner similar to thatconducted for the mask blanks. Specifically, Ta4f narrow spectra wereacquired for the highly oxidized layer 4 a, the pattern 3 a of the Taoxide layer 3, and the pattern 2 a of the Ta nitride layer 2,respectively, and compared with one another. As a result, it has beenconfirmed that the pattern 3 a of the Ta oxide layer 3 and the highlyoxidized layer 4 a had the oxygen content of 60 at % or more and thatthe oxygen content in the light-shielding film pattern 30 a increasedtowards the surface. In addition, it has been confirmed that, towardsthe surface of the light-shielding film pattern 30 a, the peak of theTa4f narrow spectrum was shifted to a higher energy side and theabundance ratio of the Ta₂O₅ bonds in the film become high.

By using each of the transfer masks according to Examples 8 to 12manufactured in the similar manner, an exposure transfer step wascarried out to transfer a transfer pattern onto a transfer object, thatis, a resist film formed on a semiconductor wafer. As an exposureapparatus, use was made of an immersion exposure type using annularillumination with an ArF excimer laser as a light source. Specifically,each of the transfer masks according to Examples 8 to 12 was set on amask stage of the exposure apparatus. For a resist film formed on eachsemiconductor wafer and adapted for ArF immersion exposure, exposuretransfer was performed. Each resist film after exposure was subjected toa predetermined development process to form a resist pattern.Thereafter, by the use of each resist pattern, a circuit pattern of DRAMhp45 nm was formed on each semiconductor wafer.

For the circuit pattern on each semiconductor wafer, cross-sectionalobservation was performed by using the STEM (Scanning TransmissionElectron Microscope). As a consequence, it was confirmed that eachsemiconductor wafer subjected to exposure transfer by using each of thetransfer masks of Examples 8 to 12 sufficiently satisfied thespecification of the circuit pattern of DRAM hp45 nm.

EXAMPLE 13 Manufacture of a Mask Blank: Heat Treatment

On a substrate 1 made of synthetic quartz and having a size of about 152mm×152 mm square and a thickness of 6.35 mm, a TaBN layer(light-shielding layer) 2 was deposited to a thickness of 47 nm by a DCmagnetron sputter apparatus. Deposition of the TaBN layer 2 wasperformed by reactive sputtering using, as a sputter target, a mixedtarget of Ta and B (Ta:B=80:20 in at % ratio) in a mixed gas atmosphereof Xe and N₂ (see FIG. 3( a)). Next, in a state where the substrate 1with the TaBN layer 2 deposited thereon was held in the sputterapparatus, a TaBO layer (front-surface antireflection layer) 3 wasdeposited to a thickness of 10 nm. Deposition of the TaBO layer 3 wasperformed by reactive sputtering using a mixed target of Ta and B in amixed atmosphere of Ar and O₂ (see FIG. 3( b)).

Thus, a light-shielding film 30 comprising the TaBN layer 2 and the TaBOlayer 3 was formed on the substrate 1. At a surface of thelight-shielding film 30 manufactured as described above, the reflectance(front-surface reflectance) was 18.5% for ArF exposure light (wavelengthof 193 nm). At a back surface of the substrate 1 without thelight-shielding film 30, the reflectance (back-surface reflectance) was33.9% for ArF exposure light. The transmittance for ArF exposure lightwas 0.1%. The light-shielding film 30 was subjected to XPS (X-rayPhotoelectron Spectroscopy) analysis. As a result, the TaBN layer 2 hada nitrogen content of 15 at %. The TaBO layer 3 had an oxygen content of61 at %. FIG. 14 shows, as a result of XPS (X-ray PhotoelectronSpectroscopy) analysis, a profile of the light-shielding film 30 in adepth direction. Subsequently, before progress of natural oxidation (forexample, within one hour after the film deposition) or after the maskblank after deposition of the light-shielding film 30 was held in anenvironment without causing natural oxidization to progress, the maskblank thus manufactured was subjected to a heat treatment (surfacetreatment) in the ambient atmosphere at a heating temperature of 200° C.for a treating time of 5 minutes. The mask blank thus manufactured wassubjected to cross-sectional observation by the use of the STEM(Scanning Transmission Electron Microscope). As a result, it has beenconfirmed from dark-field images that the light-shielding film 30 had ahighly oxidized layer 4 of 3 nm thick as a surface layer.

FIGS. 15 to 17 show Ta4f narrow spectra of the light-shielding film 30as a result of the XPS analysis. FIG. 15 shows the Ta4f narrow spectrumof an uppermost layer of the light-shielding film 30. It is seen thatthe narrow spectrum of the uppermost layer (highly oxidized layer 4) hasa high peak at a position of the binding energy of Ta₂O₅. Therefore, itis understood that the abundance ratio of Ta₂O₅ bonds is high in theuppermost layer. FIG. 16 shows a Ta4f narrow spectrum of the TaBO layer3 at a depth reached by Ar ion etching of the light-shielding film 30from its surface in a depth direction for 1.5 minutes (see FIG. 14). Inthe narrow spectrum of the TaBO layer 3, a peak appearing at a positionof the binding energy of Ta₂O₅ is superposed on another peak appearingat a position of the binding energy of Ta. As compared with the narrowspectrum of the uppermost layer, the narrow spectrum of the TaOB layer 3has the peak slightly closer to the position of the binding energy of Taand the abundance ratio of Ta₂O₅ bonds in the TaBO layer is not high.FIG. 17 shows a Ta4f narrow spectrum of the TaBN layer 2 at a depthreached by Ar ion etching of the light-shielding film 30 from itssurface in a depth direction for 11 minutes (see FIG. 14). The narrowspectrum of the TaBN layer 2 does not have a peak at a position of thebinding energy of Ta₂O₅ but has a peak near the position of the bindingenergy (21.0 eV) of Ta.

As described above, it is understood from the result of the XPS analysisfor the light-shielding film 30 of Example 13 that, even in thelight-shielding film 30 containing boron, each of the TaBO layer 3 andthe uppermost layer of the highly oxidized layer 4 has the oxygencontent of 60 at % or more and that the oxygen content in thelight-shielding film 30 increases towards the surface. Furthermore, itis obvious that, towards the surface, the peak of the Ta4f narrowspectrum is shifted to a high energy side and the abundance ratio of theTa₂O₅ bonds in the film becomes higher.

What is claimed is:
 1. A method of manufacturing a transfer mask havinga light-shielding film pattern on a transparent substrate, the methodcomprising: preparing a mask blank having a light-shielding film made ofa material containing tantalum as a main metal component on atransparent substrate; etching the light-shielding film to form thelight-shielding film pattern; and treating the light-shielding filmpattern with hot water or ozone water to form a highly oxidized layerwith an oxygen content of 60 at % or more as a surface layer of thelight-shielding film pattern.
 2. The method of manufacturing a transfermask according to claim 1, wherein the highly oxidized layer has athickness of 1.5 nm or more and 4 nm or less.
 3. The method ofmanufacturing a transfer mask according to claim 1, wherein thelight-shielding film has a structure in which at least a light-shieldinglayer and a front-surface antireflection layer are laminated in thisorder from the transparent substrate side.
 4. The method ofmanufacturing a transfer mask according to claim 3, an oxygen content ofthe front-surface antireflection layer is lower than the oxygen contentof the highly oxidized layer.
 5. The method of manufacturing a transfermask according to claim 1, wherein the highly oxidized layer has a Ta4fnarrow spectrum, when the highly oxidized layer is analyzed by X-rayphotoelectron spectroscopy, and has a maximum peak at a binding energyof more than 23 eV.
 6. The method of manufacturing a transfer maskaccording to claim 1, wherein a Ta4f narrow spectrum of thelight-shielding film, except the highly oxidized layer analyzed by X-rayphotoelectron spectroscopy, has a maximum peak at a binding energy whichequal to or less than 23 eV.
 7. A method of manufacturing asemiconductor device, comprising forming a circuit pattern on asemiconductor wafer by the use of the transfer mask manufactured by thetransfer mask manufacturing method according to claim 1.